1. Field of the Invention
The present invention relates to a conveying belt used for conveying a precision component to a predetermined position while guaranteeing very precise position accuracy, an annular, tubular, ring-shaped or belt-shaped film, such as a closed envelope for packing or accommodating an article, and a method for manufacturing the film. The present invention is mainly utilized for a functional component of an image forming apparatus. Particularly, the present invention relates to a endless belt, a method for manufacturing the endless belt, a conveying device, a tubular film, a method for manufacturing the tubular film, and an image forming apparatus.
2. Description of the Related Art
In conventional electrophotographic image forming apparatuses, an optical-information electrostatic latent image is formed on the surface of a photosensitive member by causing the photosensitive member to perform running (rotation/movement) in one direction at a constant speed and exposing optical information on the surface of the photosensitive member. Although a rotating cylindrical drum is usually used as the photosensitive member, a running endless belt is also used.
In some electrophotographic image forming apparatuses, when forming a color latent image, endless-belt conveying devices are used as a transfer-material conveying member, an intermediate transfer member, a continuous sheet conveying member and the like for mixing four-color, i.e., Y (yellow), C (cyan), M (magenta) and K (black), latent images on a recording medium.
Conventionally, a heat-roller fixing method in which a recording medium is grasped and conveyed between a heat roller and a pressing roller is used as a fixing method for fixing/solidifying a toner latent image on the recording medium has been widely used. A fixing device using a thin-film endless belt in order to shorten the warm-up time is disclosed in Japanese Patent Application Laid-Open (Kokai) No. 63-313182 (1988).
Recently, the number of image forming apparatuses using endless belts in the above-described manner is increasing. When using cylindrical drums as the above-described components, no problem arises by rotatably driving each drum around the central axis thereof. However, when running an endless belt, the problem of skew of the endless belt stretched between rollers with respect to the driving direction arises. If the skew is not corrected, a desired image cannot be formed (in formation of a latent image, image transfer, and image fixing), and problems, such as disturbance of the formed image, and the like, may arise.
There are two main approaches for preventing skew of an endless belt.
(1) In one approach, deviation or skew of an endless belt is detected by some means, and the endless belt is forcedly returned to its original running position by the tension or the centripetal force of the belt. Japanese Patent Application Laid-Open (Kokai) No. 54-69442 (1979) discloses, for example, a method of inclining a roller for driving the belt, a driven roller for stretching the belt, and the like, so as to move in a direction opposite to the moving direction of the belt. The application also discloses a method of stretching the belt between a driving roller and a driven roller, providing a swingable swinging roller contacting the inner surface of the belt at a substantially midpoint of the belt, and swinging the swinging roller in a certain direction in accordance with signals from detection means for detecting deviation of the belt which are disposed at both side portions of the belt.
However, in the above-described methods, it is necessary to use detection means, and to provide a mechanical device for inclining the roller, and extra members, such as a vibration roller and the like, which are substantially unnecessary in an image forming apparatus, resulting in an expensive configuration.
(2) In another approach, in order to inexpensively prevent skew of an endless belt, at least one rubber-band-shaped endless rib member or line-shaped rib member having end portions is mounted at one end portion or both end portions of the surface or the back of the endless belt, and skew of the endless belt is regulated by causing the rib member to contact a guide member provided at a part of each of driving and driven rollers. Methods for mounting rib members on the inner surface of an endless belt have been proposed, for example, in Japanese Patent Application Laid-Open (Kokai) No. 4-159911 (1992), and methods for mounting rib members on the outer sides of an endless belt have been proposed, for example, in Japanese Patent Application Laid-Open (Kokai) No. 1-160277 (1989).
However, in the above-described approach (2) in which skew of an endless belt is controlled by mounting rib members made of rubber or the like at at least one end portion of the endless belt, and regulating the rib members by guide members, since problems, such as deviation in color, and the like, during color-image formation (to be described later) arise, it has recently become necessary to very precisely mount ribs. As a result, very precise accuracy in the shape of rib members, such as straightness, linearity and the like, has been requested. Accordingly, the frequency of use of line-shaped rib members whose shape can be very precisely controlled compared with the case of using a rib member having the shape of an endless rubber band is increasing.
No particular problem arises when using an endless rib member. However, when using a line-shaped rib member, a small gap is formed at a connection portion formed by both ends of the rib member. If an endless belt is driven while being stretched between rollers in this sate, a stress generated by discontinuity of the rib member is applied to a belt portion positioned at the gap of the rib member every time the gap passes through the roller portions, resulting in repeated application of load at that belt portion more than at other portions. As a result, the belt tends to destruct or break at the connection portion.
In order to prevent such problems, approaches of dispersing concentration of the stress, for example, by obliquely cutting the end surface of the rib member at the connection portion, or making the end surfaces of the rib in the shape of a hook have been devised. However, many problems are present, for example, in the provision of a device for cutting the end surfaces of the rib obliquely or in the shape of a hook, and accuracy in bonding at the connection portion.
It is an object of the present invention to provide an endless belt, a method for manufacturing the endless belt, a conveying device, a tubular film, a method for manufacturing the tubular film, and an image forming apparatus, in which high durability is obtained by suppressing skew of each of the above-described components.
According to one aspect, the present invention which achieves the above-described object relates to an endless belt including at least one rib member, whose both end surfaces face each other, provided on an inner circumferential surface of the endless belt. The endless belt is stretched between at least two rollers and driven while contacting the at least one rib member to side surfaces of the at least two rollers. A first distance from a lateral-direction end, serving as an end of the endless belt in a lateral direction, which is closer to a side where the at least one rib member is provided, to a side surface of the at least one rib member at a side closer to the lateral-direction end is longer than a second distance, serving as an interval of a gap portion formed by the facing end surfaces of the at least one rib member.
In the endless belt according to the present invention configured in the above-described manner, since the rib member is formed at a position where concentration of stress generated in the endless belt at the gap portion of the rib member does not influence the lateral-direction end of the endless belt, breakage of the endless belt from the lateral-direction end near the gap portion due to concentration of the stress generated in the endless belt at the gap portion can be suppressed for a long time.
Preferably, the first distance is longer than the second distance by at least twice. A cross-section of the at least one rib member may be a rectangle, and a hardness of the at least one rib member may be smaller than a hardness of the endless belt.
According to another aspect, the present invention which achieves the above-described object relates to a method for manufacturing an endless belt including at least one rib member, whose both end surfaces face each other, provided on an inner circumferential surface of the endless belt. The endless belt is stretched between at least two rollers and driven while contacting the at least one rib member to side surfaces of the at least two rollers. The method includes the step of forming a groove for mounting the at least one rib member at a position where a first distance from a lateral-direction end, serving as an end of the endless belt in a lateral direction, to a side surface of the at least one rib member at a side closer to the lateral-direction end is longer than a second distance, serving as an interval of a gap portion formed by the facing end surfaces of the at least one rib member.
In the above-described method for manufacturing the endless belt according to the present invention, the groove for mounting the rib member is formed at a position where concentration of stress generated in the endless belt at the gap portion of the rib member does not influence the lateral-direction end of the endless belt. Hence, in the endless belt manufactured in the above-described method, breakage of the endless belt from the lateral-direction end near the gap portion due to concentration of the stress generated in the endless belt at the gap portion is prevented for a long time.
The method for manufacturing the endless belt according to the present invention preferably includes the step of forming the first distance so as to be longer than the second distance by at least twice. The method may include the step of forming a cross-section of the at least one rib member to be a rectangle, and may include the step of forming the at least one rib member with a material whose hardness is smaller than a hardness of the endless belt.
According to still another aspect, the present invention which achieves the above-described object relates to a conveying device including a conveying belt stretched between at least two rollers, and driving means for driving at least one of the rollers. The conveying device conveys a sheet material mounted on the conveying belt. The conveying belt is one of the above-described endless belts.
In the conveying device according to the present invention configured in the above-described manner, since the endless belt according to the present invention is used as the conveying belt, breakage of the conveying belt from the lateral-direction end near the gap portion due to concentration of the stress generated in the conveying belt at the gap portion is prevented for a long time.
According to yet another aspect, the present invention which achieves the above-described object relates to a tubular film including at least one rib member, whose both end surfaces face each other, provided on an inner circumferential surface of the tubular film, and rotatably driven while contacting the at least one rib member to an external regulating member. A first distance from a lateral-direction end, serving as an end of the tubular film in a lateral direction, which is closer to a side where the at least one rib member is provided, to a side surface of the at least one rib member at a side closer to the lateral-direction end is longer than a second distance, serving as an interval of a gap portion formed by the facing end surfaces of the rib at least one member.
In the tubular film according to the present invention configured in the above-described manner, since the rib member is formed at a position where concentration of a stress generated in the tubular film at the gap portion of the rib member does not influence the lateral-direction end of the tubular film, breakage of the tubular film from the lateral-direction end near the gap portion due to concentration of the stress generated in the tubular film at the gap portion can be suppressed for a long time.
Preferably, the first distance is longer than the second distance by at least twice. A cross-section of the at least one rib member may be a rectangle, and a hardness of the at least one rib member may be smaller than a hardness of the endless belt.
According to yet a further aspect, the present invention which achieves the above-described object relates to a method for manufacturing a tubular film including at least one rib member, whose both end surfaces face each other, provided on an inner circumferential surface of the tubular film, and rotatably driven while contacting the at least one rib member to an external regulating member. The method includes the step of forming a groove for mounting the at least one rib member at a position where a first distance from a lateral-direction end, serving as an end of the tubular film in a lateral direction, which is closer to a side where the at least one rib member is provided, to a side surface of the rib member at a side closer to the lateral-direction end is longer than a second distance, serving as an interval of a gap portion formed by the facing end surfaces of the at least one rib member.
The method for manufacturing the tubular film according to the present invention preferably includes the step of forming the first distance so as to be longer than the second distance by at least twice. The method may include the step of forming a cross-section of the at least one rib member to be a rectangle, and may include the step of forming the at least one rib member with a material whose hardness is smaller than a hardness of the endless belt.
According to still another aspect, the present invention which achieves the above-described object relates to an electrophotographic image forming apparatus including a conveying belt, and a fixing device. A latent image is formed on a surface of a charged photosensitive drum by scanning the surface with a laser beam, a toner is caused to adhere to the latent image, the toner is then transferred onto a recording material on the conveying belt, and the toner is fixed by the fixing device. The conveying belt is one of the above-described endless belts.
In the image forming apparatus according to the present invention configured in the above-described manner, since the endless belt according to the present invention is used as the conveying belt, breakage of the conveying belt from the lateral-direction end near the gap portion due to concentration of the stress generated in the conveying belt at the gap portion is prevented for a long time.
The image forming apparatus according to the present invention may further include an intermediate belt for performing, after primary transfer of the toner adhering to the photosensitive drum, secondary transfer of the toner subjected to the primary transfer, onto the recording material. The intermediate belt may be one of the above-described endless belts. The fixing device may include a pressing roller and one of the above-described tubular films.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.